This invention pertains to an air-hydraulic pump having a fluid motor utilizing a reciprocal piston carrying control valve means and with structure provided to prevent inadvertent stalling of the piston of the air-motor.
An air-hydraulic pump wherein a fluid motor drives a pumping member is shown in McClocklin U.S. Pat. No. 3,597,121, owned by the assignee of this application. Pumps of this type have been in extensive use for a number of years. The air-hydraulic pump has an air-motor including a reciprocal piston which is driven in one direction by fluid under pressure and is returned by a spring. The cycling of the air-motor is under the control of control valve means movably mounted within the piston. The valve means is in open position during the return stroke of the piston to a retracted position thereof and the pumping stroke of the piston to an extended position relies upon closing of the valve means by physical contact thereof with an end wall of the cylinder mounting the piston. Normally, the piston will contact the end wall of the cylinder at the end of the return stroke and it is possible to have a rebounding action thereof which can inadvertently cause the valve means to move from closed to open position, with the result that the piston can stall, which terminates the operation of the pump.